PhD ThesisA single doubly-fed induction machine (SDFM) is a wound rotor induction machine with
the stator connected to a supply network and the rotor fed by a bi-directional converter. A
cascaded doubly-fed induction machine (CDFM) is a. connection of two wound rotor
induction machines with the rotors connected electrically and mechanically thus avoiding
brushes. One stator is connected to the supply network and the other is fed by a bidirectional
converter. Both schemes, the SDFM and the CDFM, have in common that the
VA-rating of the power converter is reduced compared to a singly-fed system. This thesis
presents investigations of the field oriented control for the SDFM and the CDFM. -
After reviewing and categorising doubly-fed machines a thorough steady state analysis and
stator flux oriented control treatment of the SDFM is presented. Although the steady state
analysis and the field oriented control of a SDFM is well established it is necessary that this
is included as foundation for the CDFM control behaviour and for the sensorless control
investigations.
Steady state analysis of the CDFM highlights similarities to the SDFM. Two different field
oriented control schemes are applied to the CDFM. A previously developed combined flux
oriented scheme is modified to be applicable to a CDFM consisting of any machine
combination. Furthermore, the scheme is simplified by removing a mathematical control
extension in the q-axis, which has a stabilising effect on the control performance.
Justified by steady state analysis the stator flux oriented control structure initially developed
for the SDFM is applied to the CDFM.
Two variations of a position sensorless scheme taking advantage of the proportionalitics
between stator and rotor quantities are applied to the SDFM. Differentiating the estimated
position angle allows the schemes to be extended for speed control purposes.
The performance of the scnsorless field oriented control methods are also investigated on
the CDFM.
Harmonic analysis of the SDFM / CDFM systeme stablishes harmonic sources and harmonic
current propagation through the system. A theoretical harmonic current prediction process
incorporating simulation and steady state modeling delivers good results.
All theoretical investigations are confirmed by experimental results. The experimental realtime
controlled drive system consists of two 2.25 kW wound rotor induction machines, a bidirectional
IGBT converter and the control hardware comprises two 8OC167
microcontrollers.Department of Electrical and Electronic Engineerin